This invention relates to electric power utility networks including generating systems, transmission systems, and distribution systems serving loads.
Utility power systems, particularly at the transmission level, are primarily inductive, due to the impedance of transmission lines and the presence of numerous transformers. Further, many of the largest loads connected to the utility power system are typically inductive. Large motors used, for example, in lumber mills, rock crushing plants, steel mills, and to drive pumps, shift the power factor of the system away from the desired unity level, thereby decreasing the efficiency of the power system. Because of the daily and hourly load variations, it is necessary to change the amount of compensation applied to counteract the effects of these changing inductive loads
One approach for providing compensation to the system is to connect one or more large shunt capacitor banks to provide a capacitive reactance (e.g., as much as 36 MVARs) to the system in the event of a contingency (i.e., a nonscheduled event or interruption of service) or sag in the nominal voltage detected on the utility power system. By selecting the proper amount of capacitance and connection location, these capacitor banks provide a level of control of the line voltage or power factor. Mechanical contactors are typically employed to connect and switch the capacitor banks to compensate for the changing inductive loads.